1. Technical Field
The present invention generally relates to the field of digital signal processing, and more specifically, to a system and method for digital watermarking.
2. Description of the Related Art
In recent years, the digital watermarking technology has been widely applied in fields such as copyright protection of multimedia digital signals, release control, consistency check, broadcast monitoring, data hiding, etc. The basic idea of the digital watermarking technology is adding information called watermark into digital multimedia signals such as image, graph, audio and/or video, so as to be used for various verification purposes in the future. The watermark is substantively a digital signature hidden in a main multimedia signal, providing information such as proprietorship or rights of use of the main multimedia signals.
From the perspective of extraction and detection of a watermark, the watermarking technology may be divided into non-blind watermarking technology, semi-blind watermarking technology, and blind watermarking technology. Upon extract and decoding, the non-blind watermarking technology needs the original multimedia information and the added reference signals (e.g., pseudo noise sequence); upon extraction, the semi-blind watermarking technology needs a reference signal and a key for generating the reference signal; the blind watermarking technology only needs the key in the case of extraction.
In the digital watermarking technology for audio, a spread spectrum (SS)-modulated digital watermark is a known blind watermarking technology. However, the traditional SS-based watermark only considers the influence of attacking noise on watermark decoding, which ignores the interference to watermark decoding introduced by the main audio signal per se, which causes increase of the bit error rate. Moreover, in order to lower the auditory distortion caused by the watermark to main audio signals, the watermark embedding party always performs spectrum processing to the reference signals in use, such that a digital watermark decoder performing blind detection can hardly recover the reference signals used by the watermark embedding party accurately. In other words, reference signal mismatch exists between the watermark embedding party and the decoder party, which causes deterioration of the decoding performance.
Therefore, a more accurate and robust digital audio watermarking technology is needed in this field.